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CALCIUM CITRATE

59

in powdering the sample rapidly and then decomposing two or more aliquot
parts of the powder.

. 4. Purity of the Acetylene.—The acetylene may contain various
impurities, such as hydrogen phosphide and sulphide, ammonia, hydrogen,
nitrogen, oxygen and carbonic oxide. Of these the most important to
detect and estimate is hydrogen phosphide. Lunge and Cedercreutz's
method may be used for this purpose : 50 grams of the carbide are placed
in a flask of about J litre capacity closed by a stopper with two holes, through
one of which passes a tapped funnel and through the other a right-angled tube
connected with a tube with 10 bulbs into which are poured 75 c.c. of 2-3%
sodium hypochlorite solution. From the funnel water is dropped slowly
on to the carbide, which is occasionally shaken. When the evolution of
gas ceases, the flask is nearly filled with water and gentle suction applied
to the bulb-tube, so that all the gas traverses the hypochlorite. The con-
tents of the bulb-tube are then introduced into a beaker and the phosphoric
acid (formed by the action of the hypochlorite on the hydrogen phosphide)
precipitated with magnesia mixture (see Fertilisers). I gram of magnesium
pyrophosphate = 0-81982 gram of calcium phosphide (Ca3P2) =200-86
c.c. of hydrogen phosphide (PH3).

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* *

Commercial calcium carbide in lumps or pieces should not contain more
than 5% of fine dust passing through a sieve of i mm. mesh, and the impurities
should not exceed 3-6%. Good carbide usually gives about 300 litres (at 15° and
760 mm.) of acetylene per kilo, whilst the chemically pure product should give
348-8 litres. A commercial carbide should not give less than 270 litres per kilo,
with an allowance of 2% on the analytical results. The impurities in the gas
should not exceed i%. Of these hydrogen sulphide or ammonia is found rarely
and only in traces, but hydrogen phosphide occurs in relatively large propor-
tions ; Lunge and Cedercreutz have found from 0-031 to 0-061% by volume,
which would correspond with about o-038-o-o75 gram of calcium phosphide
per kilo of carbide (with a yield of 300 litres of gas).

CALCIUM   CITRATE

Crude calcium citrate, prepared largely in Sicily, serves as raw material
for the preparation of citric acid. It forms yellowish-grey clots or powder
with a slight biscuity odour and dissolves slightly in cold water with an
alkaline reaction and still less in hot water. It consists mostly of calcium
citrate, mixed with calcium carbonate and oxide, with small proportions
of other salts and organic compounds of calcium, ferric oxide, alumina,
silica, etc. ; in some cases it contains magnesia and strontia.

The commercial value of calcium citrate depends on the quantity of
crystallised citric acid corresponding with the pure calcium citrate con-
tained in the product. The quantitative estimation of the citric acid
hence occupies first place in the analysis ; then come determinations of
the alkalinity, hygroscopic moisture and ash, and a partial qualitative
analysis to detect any such adulteration as sulphate, oxalate, phosphate,
tartrate of calcium, etc.. of the amyl acetate